> Aztec.nr API reference, v6.0.0 (mainnet and testnet). Index: https://docs.aztec.network/aztec-nr-api/mainnet/llms.txt

# Struct PublicContext

Module: `noir_aztec::context`

```rust
pub struct PublicContext
{ /* private fields */ }
```

## PublicContext

The **main interface** between an #\[external("public")] function and the Aztec blockchain.

An instance of the PublicContext is initialized automatically at the outset of every public function, within the #\[external("public")] macro, so you'll never need to consciously instantiate this yourself.

The instance is always named `context`, and it will always be available within the body of every #\[external("public")] function in your smart contract.

Typical usage for a smart contract developer will be to call getter methods of the PublicContext.

*Pushing* data and requests to the context is mostly handled within aztec-nr's own functions, so typically a smart contract developer won't need to call any setter methods directly.

## Responsibilities

- Exposes contextual data to a public function:
- Data relating to how this public function was called:
- msg_sender, this_address
- Data relating to the current blockchain state:
- timestamp, block_number, chain_id, version
- Gas and fee information
- Provides state access:
- Read/write public storage (key-value mapping)
- Check existence of notes and nullifiers (Some patterns use notes & nullifiers to store public (not private) information)
  - Enables consumption of L1->L2 messages.
- Enables calls to other public smart contract functions:
- Writes data to the blockchain:
- Updates to public state variables
- New public logs (for events)
  - New L2->L1 messages
- New notes & nullifiers (E.g. pushing public info to notes/nullifiers, or for completing "partial notes")

## Key Differences from Private Execution

Unlike private functions -- which are executed on the user's device and which can only reference historic state -- public functions are executed by a block proposer and are executed "live" on the *current* tip of the chain. This means public functions can:

- Read and write *current* public state
- Immediately see the effects of earlier transactions in the same block

Also, public functions are executed within a zkVM (the "AVM"), so that they can *revert* whilst still ensuring payment to the proposer and prover. (Private functions cannot revert: they either succeed, or they cannot be included).

## Optimising Public Functions

Using the AVM to execute public functions means they compile down to "AVM bytecode" instead of the ACIR that private functions (standalone circuits) compile to. Therefore the approach to optimising a public function is fundamentally different from optimising a public function.

## Implementations

```rust
impl PublicContext
```

```rust
pub fn new(compute_args_hash: fn() -> Field) -> Self
```

Creates a new PublicContext instance.

Low-level function: This is called automatically by the #\[external("public")] macro, so you shouldn't need to be called directly by smart contract developers.

#### Arguments

- `compute_args_hash` - Function to compute the args_hash

#### Returns

- A new PublicContext instance

```rust
pub fn emit_public_log_unsafe<T>(_self: Self, tag: Field, log: T)
where
    T: Serialize
```

Emits a *public* log that will be visible onchain to everyone.

#### Arguments

- `tag` - A tag placed at `fields[0]` of the emitted log. Nodes index logs by this value, allowing clients to efficiently query for matching logs without scanning all of them.
- `log` - The data to log, must implement Serialize trait.

#### Safety

The `tag` should be domain-separated (e.g. via [`crate::protocol::hash::compute_log_tag`](/aztec-nr-api/mainnet/protocol_types/hash/fn.compute_log_tag.md)) to prevent collisions between logs from different sources. Without domain separation, two unrelated log types that happen to share a raw tag value become indistinguishable. Prefer `self.emit(event)` for events, which handles tagging automatically.

```rust
pub fn note_hash_exists(_self: Self, note_hash: Field, leaf_index: u64) -> bool
```

Checks if a given note hash exists in the note hash tree at a particular leaf_index.

#### Arguments

- `note_hash` - The note hash to check for existence
- `leaf_index` - The index where the note hash should be located

#### Returns

- `bool` - True if the note hash exists at the specified index

```rust
pub fn l1_to_l2_msg_exists(_self: Self, msg_hash: Field, msg_leaf_index: Field) -> bool
```

Checks if a specific L1-to-L2 message exists in the L1-to-L2 message tree at a particular leaf index.

Common use cases include token bridging, cross-chain governance, and triggering L2 actions based on L1 events.

This function should be called before attempting to consume an L1-to-L2 message.

#### Arguments

- `msg_hash` - Hash of the L1-to-L2 message to check
- `msg_leaf_index` - The index where the message should be located

#### Returns

- `bool` - True if the message exists at the specified index

#### Advanced

- Uses the AVM l1_to_l2_msg_exists opcode for tree lookup
- Messages are copied from L1 Inbox to L2 by block proposers

```rust
pub fn nullifier_exists_unsafe(
    _self: Self,
    unsiloed_nullifier: Field,
    contract_address: AztecAddress,
) -> bool
```

Returns `true` if an `unsiloed_nullifier` has been emitted by `contract_address`.

Note that unsiloed nullifiers are not the actual values stored in the nullifier tree: they are first siloed via [`crate::hash::compute_siloed_nullifier`](/aztec-nr-api/mainnet/protocol_types/hash/fn.compute_siloed_nullifier.md) with the emitting contract's address.

#### Use Cases

Nullifiers are typically used as a *privacy-preserving* record of a one-time action, but they can also be used to efficiently record *public* one-time actions as well. This is cheaper than using public storage, and has the added benefit of the nullifier being emittable from a private function.

An example is to check whether a contract has been published: we emit a nullifier that is deterministic and which has a *public* preimage.

#### Public vs Private

In general, one should not attempt to prove nullifier non-existence in private, as that will not consider the possibility of the nullifier having been emitted in any transaction between the anchor block and the inclusion block. Private functions instead prove existence via [`crate::context::PrivateContext::assert_nullifier_exists`](/aztec-nr-api/mainnet/noir_aztec/context/struct.PrivateContext.md#assert_nullifier_exists) and 'prove' non-existence by *emitting* the nullifer, which would cause the transaction to fail if the nullifier existed.

This is not the case in public functions, which **do** have access to the tip of the blockchain and so can reliably prove whether a nullifier exists or not.

#### Safety

While it is safe to rely on this function's return value to determine if a nullifier exists or not, it is often **not** safe to infer additional information from that. In particular, it is **unsafe** to infer that the existence of a nullifier emitted from a private function implies that all other side-effects of said private execution have been completed, more concretely that any enqueued public calls have been executed.

For example, if a function in contract `A` privately emits nullifier `X` and then enqueues public function `Y`, then it is **unsafe** for a contract `B` to infer that `Y` has alredy executed simply because `X` exists.

This is because **all** private transaction effects are committed *before* enqueued public functions are run (in order to not reveal detailed timing information about the transaction), so it is possible to observe a nullifier that was emitted alongside the enqueuing of a public call **before** said call has been completed.

#### Cost

This emits the `CHECKNULLIFIEREXISTS` opcode, which conceptually performs a merkle inclusion proof on the nullifier tree (both when the nullifier exists and when it doesn't).

```rust
pub fn consume_l1_to_l2_message<let N: u32>(
    self,
    content: Field,
    secret: [Field; N],
    sender: EthAddress,
    leaf_index: Field,
)
```

Consumes a message sent from Ethereum (L1) to Aztec (L2) -- effectively marking it as "read".

Use this function if you only want the message to ever be "referred to" once. Once consumed using this method, the message cannot be consumed again, because a nullifier is emitted. If your use case wants for the message to be read unlimited times, then you can always read any historic message from the L1-to-L2 messages tree, using the `l1_to_l2_msg_exists` method. Messages never technically get deleted from that tree.

The message will first be inserted into an Aztec "Inbox" smart contract on L1. It will not be available for consumption immediately. Messages get copied-over from the L1 Inbox to L2 by the next Proposer in batches. So you will need to wait until the messages are copied before you can consume them.

#### Arguments

- `content` - The message content that was sent from L1
- `secret` - Secret fields used for message privacy (if needed)
- `sender` - Ethereum address that sent the message
- `leaf_index` - Index of the message in the L1-to-L2 message tree

#### Advanced

- Validates message existence in the L1-to-L2 message tree
- Prevents double-consumption by emitting a nullifier
- Message hash is computed from all parameters + chain context
- Will revert if message doesn't exist or was already consumed

```rust
pub fn message_portal(_self: Self, recipient: EthAddress, content: Field)
```

Sends an "L2 -> L1 message" from this function (Aztec, L2) to a smart contract on Ethereum (L1). L1 contracts which are designed to send/receive messages to/from Aztec are called "Portal Contracts".

Common use cases include withdrawals, cross-chain asset transfers, and triggering L1 actions based on L2 state changes.

The message will be inserted into an Aztec "Outbox" contract on L1, when this transaction's block is proposed to L1. Sending the message will not result in any immediate state changes in the target portal contract. The message will need to be manually consumed from the Outbox through a separate Ethereum transaction: a user will need to call a function of the portal contract -- a function specifically designed to make a call to the Outbox to consume the message. The message will only be available for consumption once the *epoch* proof has been submitted. Given that there are multiple Aztec blocks within an epoch, it might take some time for this epoch proof to be submitted -- especially if the block was near the start of an epoch.

#### Arguments

- `recipient` - Ethereum address that will receive the message
- `content` - Message content (32 bytes as a Field element)

```rust
pub unconstrained fn call_public_function<let N: u32>(
    _self: Self,
    contract_address: AztecAddress,
    function_selector: FunctionSelector,
    args: [Field; N],
    gas_opts: GasOpts,
) -> [Field]
```

Calls a public function on another contract.

Will revert if the called function reverts or runs out of gas.

#### Arguments

- `contract_address` - Address of the contract to call
- `function_selector` - Function to call on the target contract
- `args` - Arguments to pass to the function
- `gas_opts` - An optional allocation of gas to the called function.

#### Returns

- `[Field]` - Return data from the called function

```rust
pub unconstrained fn static_call_public_function<let N: u32>(
    _self: Self,
    contract_address: AztecAddress,
    function_selector: FunctionSelector,
    args: [Field; N],
    gas_opts: GasOpts,
) -> [Field]
```

Makes a read-only call to a public function on another contract.

This is similar to Solidity's `staticcall`. The called function cannot modify state or emit events. Any nested calls are constrained to also be staticcalls.

Useful for querying data from other contracts safely.

Will revert if the called function reverts or runs out of gas.

#### Arguments

- `contract_address` - Address of the contract to call
- `function_selector` - Function to call on the target contract
- `args` - Array of arguments to pass to the called function
- `gas_opts` - An optional allocation of gas to the called function.

#### Returns

- `[Field]` - Return data from the called function

```rust
pub fn push_note_hash(_self: Self, note_hash: Field)
```

Adds a new note hash to the Aztec blockchain's global Note Hash Tree.

Notes are ordinarily constructed and emitted by *private* functions, to ensure that both the content of the note, and the contract that emitted the note, stay private.

There are however some useful patterns whereby a note needs to contain *public* data. The ability to push a new note_hash from a *public* function means that notes can be injected with public data immediately -- as soon as the public value is known. The slower alternative would be to submit a follow-up transaction so that a private function can inject the data. Both are possible on Aztec.

Search "Partial Note" for a very common pattern which enables a note to be "partially" populated with some data in a *private* function, and then later "completed" with some data in a public function.

#### Arguments

- `note_hash` - The hash of the note to add to the tree

#### Advanced

- The note hash will be siloed with the contract address by the protocol

```rust
pub fn push_nullifier_unsafe(_self: Self, nullifier: Field)
```

Creates a new [nullifier](/aztec-nr-api/mainnet/noir_aztec/nullifier/index.md).

While nullifiers are primarily intended as a *privacy-preserving* record of a one-time action, they can also be used to efficiently record *public* one-time actions. This function allows creating nullifiers from public contract functions, which behave just like those created from private functions.

#### Safety

This is a low-level function that must be used with great care to avoid subtle corruption of contract state.

In particular, callers must ensure all nullifiers created by a contract are properly domain-separated, so that unrelated components don't interfere with one another (e.g. a transaction nullifier accidentally marking a variable as initialized). Note nullifiers should only be created via [`crate::context::PrivateContext::push_nullifier_for_note_hash`](/aztec-nr-api/mainnet/noir_aztec/context/struct.PrivateContext.md#push_nullifier_for_note_hash).

#### Advanced

The raw `nullifier` is not what is inserted into the Aztec state tree: it will be first siloed by contract address via [`crate::protocol::hash::compute_siloed_nullifier`](/aztec-nr-api/mainnet/protocol_types/hash/fn.compute_siloed_nullifier.md) in order to prevent accidental or malicious interference of nullifiers from different contracts.

```rust
pub fn this_address(_self: Self) -> AztecAddress
```

Returns the address of the current contract being executed.

This is equivalent to `address(this)` in Solidity (hence the name). Use this to identify the current contract's address, commonly needed for access control or when interacting with other contracts.

#### Returns

- `AztecAddress` - The contract address of the current function being executed.

```rust
pub fn maybe_msg_sender(_self: Self) -> Option<AztecAddress>
```

Returns the contract address that initiated this function call.

This is similar to `msg.sender` in Solidity (hence the name).

Important Note: If the calling function is a *private* function, then it had the option of hiding its address when enqueuing this public function call. In such cases, this method will return `Option<AztecAddress>::none`. If the calling function is a *public* function, it will always return an `Option<AztecAddress>::some` (i.e. a non-null value).

#### Returns

- `Option<AztecAddress>` - The address of the smart contract that called this function (be it an app contract or a user's account contract).

#### Advanced

- Value is provided by the AVM sender opcode
- In nested calls, this is the immediate caller, not the original transaction sender

```rust
pub fn selector(_self: Self) -> FunctionSelector
```

Returns the function selector of the currently-executing function.

This is similar to `msg.sig` in Solidity, returning the first 4 bytes of the function signature.

#### Returns

- `FunctionSelector` - The 4-byte function identifier

#### Advanced

- Extracted from the first element of calldata
- Used internally for function dispatch in the AVM

```rust
pub fn get_args_hash(self) -> Field
```

Returns the hash of the arguments passed to the current function.

Very low-level function: The #\[external("public")] macro uses this internally. Smart contract developers typically won't need to access this directly as arguments are automatically made available.

#### Returns

- `Field` - Hash of the function arguments

```rust
pub fn transaction_fee(_self: Self) -> Field
```

Returns the "transaction fee" for the current transaction. This is the final tx fee that will be deducted from the fee_payer's "fee-juice" balance (in the protocol's Base Rollup circuit).

#### Returns

- `Field` - The actual, final cost of the transaction, taking into account: the actual gas used during the setup and app-logic phases, and the fixed amount of gas that's been allocated by the user for the teardown phase. I.e. effectiveL2FeePerGas \* l2GasUsed + effectiveDAFeePerGas \* daGasUsed

This will return `0` during the "setup" and "app-logic" phases of tx execution (because the final tx fee is not known at that time). This will only return a nonzero value during the "teardown" phase of execution, where the final tx fee can actually be computed.

Regardless of *when* this function is called during the teardown phase, it will always return the same final tx fee value. The teardown phase does not consume a variable amount of gas: it always consumes a pre-allocated amount of gas, as specified by the user when they generate their tx.

```rust
pub fn chain_id(_self: Self) -> Field
```

Returns the chain ID of the current network.

This is similar to `block.chainid` in Solidity. Returns the unique identifier for the blockchain network this transaction is executing on.

Helps prevent cross-chain replay attacks. Useful if implementing multi-chain contract logic.

#### Returns

- `Field` - The chain ID as a field element

```rust
pub fn version(_self: Self) -> Field
```

Returns the Aztec protocol version that this transaction is executing under. Different versions may have different rules, opcodes, or cryptographic primitives.

This is similar to how Ethereum has different EVM versions.

Useful for forward/backward compatibility checks

Not to be confused with contract versions; this is the protocol version.

#### Returns

- `Field` - The protocol version as a field element

```rust
pub fn block_number(_self: Self) -> u32
```

Returns the current block number.

This is similar to `block.number` in Solidity.

Note: the current block number is only available within a public function (as opposed to a private function).

Note: the time intervals between blocks should not be relied upon as being consistent:

- Timestamps of blocks fall within a range, rather than at exact regular intervals.
- Slots can be missed.
- Protocol upgrades can completely change the intervals between blocks (and indeed the current roadmap plans to reduce the time between blocks, eventually). Use `context.timestamp()` for more-reliable time-based logic.

#### Returns

- `u32` - The current block number

```rust
pub fn timestamp(_self: Self) -> u64
```

Returns the timestamp of the current block.

This is similar to `block.timestamp` in Solidity.

All functions of all transactions in a block share the exact same timestamp (even though technically each transaction is executed one-after-the-other).

Important note: Timestamps of Aztec blocks are not at reliably-fixed intervals. The proposer of the block has some flexibility to choose a timestamp which is in a valid *range*: Obviously the timestamp of this block must be strictly greater than that of the previous block, and must must be less than the timestamp of whichever ethereum block the aztec block is proposed to. Furthermore, if the timestamp is not deemed close enough to the actual current time, the committee of validators will not attest to the block.

#### Returns

- `u64` - Unix timestamp in seconds

```rust
pub fn min_fee_per_l2_gas(_self: Self) -> u128
```

Returns the fee per unit of L2 gas for this transaction (aka the "L2 gas price"), as chosen by the user.

L2 gas covers the cost of executing public functions and handling side-effects within the AVM.

#### Returns

- `u128` - Fee per unit of L2 gas

Wallet developers should be mindful that the choice of gas price (which is publicly visible) can leak information about the user, e.g.:

- which wallet software the user is using;
- the amount of time which has elapsed from the time the user's wallet chose a gas price (at the going rate), to the time of tx submission. This can give clues about the proving time, and hence the nature of the tx.
- the urgency of the transaction (which is kind of unavoidable, if the tx is indeed urgent).
- the wealth of the user.
- the exact user (if the gas price is explicitly chosen by the user to be some unique number like 0.123456789, or their favorite number). Wallet devs might wish to consider fuzzing the choice of gas price.

```rust
pub fn min_fee_per_da_gas(_self: Self) -> u128
```

Returns the fee per unit of DA (Data Availability) gas (aka the "DA gas price").

DA gas covers the cost of making transaction data available on L1.

See the warning in `min_fee_per_l2_gas` for how gas prices can be leaky.

#### Returns

- `u128` - Fee per unit of DA gas

```rust
pub fn l2_gas_left(_self: Self) -> u32
```

Returns the remaining L2 gas available for this transaction.

Different AVM opcodes consume different amounts of gas.

#### Returns

- `u32` - Remaining L2 gas units

```rust
pub fn da_gas_left(_self: Self) -> u32
```

Returns the remaining DA (Data Availability) gas available for this transaction.

DA gas is consumed when emitting data that needs to be made available on L1, such as public logs or state updates. All of the side-effects from the private part of the tx also consume DA gas before execution of any public functions even begins.

#### Returns

- `u32` - Remaining DA gas units

```rust
pub fn is_static_call(_self: Self) -> bool
```

Checks if the current execution is within a staticcall context, where no state changes or logs are allowed to be emitted (by this function or any nested function calls).

#### Returns

- `bool` - True if in staticcall context, false otherwise

```rust
pub fn raw_storage_read<let N: u32>(self, storage_slot: Field) -> [Field; N]
```

Reads raw field values from public storage. Reads N consecutive storage slots starting from the given slot.

Very low-level function. Users should typically use the public state variable abstractions to perform reads: PublicMutable & PublicImmutable.

#### Arguments

- `storage_slot` - The starting storage slot to read from

#### Returns

- `[Field; N]` - Array of N field values from consecutive storage slots

#### Generic Parameters

- `N` - the number of consecutive slots to return, starting from the `storage_slot`.

```rust
pub fn storage_read<T>(self, storage_slot: Field) -> T
where
    T: Packable
```

Reads a typed value from public storage.

Low-level function. Users should typically use the public state variable abstractions to perform reads: PublicMutable & PublicImmutable.

#### Arguments

- `storage_slot` - The storage slot to read from

#### Returns

- `T` - The deserialized value from storage

#### Generic Parameters

- `T` - The type that the caller expects to read from the `storage_slot`.

```rust
pub fn raw_storage_write<let N: u32>(
    _self: Self,
    storage_slot: Field,
    values: [Field; N],
)
```

Writes raw field values to public storage. Writes to N consecutive storage slots starting from the given slot.

Very low-level function. Users should typically use the public state variable abstractions to perform writes: PublicMutable & PublicImmutable.

Public storage writes take effect immediately.

#### Arguments

- `storage_slot` - The starting storage slot to write to
- `values` - Array of N Fields to write to storage

```rust
pub fn storage_write<T>(self, storage_slot: Field, value: T)
where
    T: Packable
```

Writes a typed value to public storage.

Low-level function. Users should typically use the public state variable abstractions to perform writes: PublicMutable & PublicImmutable.

#### Arguments

- `storage_slot` - The storage slot to write to
- `value` - The typed value to write to storage

#### Generic Parameters

- `T` - The type to write to storage.

## Trait implementations

```rust
impl Empty for PublicContext
```

```rust
pub fn empty() -> Self
```

```rust
pub fn is_empty(self: Self) -> bool
where
    Self: Eq
```

```rust
pub fn assert_empty<let S: u32>(self: Self, msg: str<S>)
where
    Self: Eq
```

```rust
impl Eq for PublicContext
```

```rust
pub fn eq(self, other: Self) -> bool
```